The invention relates to methods and apparatuses for performing multiplexing functions on groups of optical signals, and performing demultiplexing functions on multi-channel optical signals.
It is a common demultiplexing problem in optical systems to have an optical signal containing multiple wavelengths each at a different wavelength from which one or more individual channels must be extracted. The traditional solution to this problem has been to employ a wavelength specific demultiplexing device to extract the required wavelengths. Referring to FIG. 1, shown is an example of such a wavelength specific demultiplexer, generally indicated by 11. The input to the demultiplexer is a group of wavelengths having wavelength xcex1, . . . , xcex64. In order to extract four particular wavelengths, xcexA, xcexB, xcexC, xcexD, the demultiplexer 11 is provided which extracts those specific wavelengths and passes them to respective receivers 12, 14, 16 and 18. The demultiplexer 11 is specifically designed for the particular wavelengths xcexA, xcexB, xcexC, xcexD which are being extracted. Typically the demultiplexer 11 and four receivers 12, 14, 16 and 18 might be delivered on a card 10. In order to allow the demultiplexing of any arbitrary four wavelengths from a set of a possible 64, it would be necessary to inventory 635, 376 different such cards. More realistically perhaps, given the recent propensity towards grouping wavelengths into bands of consecutive wavelengths, in order to allow the demultiplexing of any consecutive group of four wavelengths in a 64 wavelength system, for example {xcex1, . . . xcex4}, {xcex5, . . . xcex8}, . . . , {xcex61, . . . , xcex64} there would be a requirement to inventory 16 different demultiplexer cards.
This same problem exists on the multiplexing side, namely that a large number of wavelength specific devices must be manufactured and inventoried in order to provide multiplexing flexibility.
Methods and devices are provided for optical demultiplexing and optical multiplexing.
One broad aspect of the invention provides an optical wavelength demultiplexer adapted to perform wavelength demultiplexing of an input optical signal containing a plurality of wavelengths. The demultiplexer has a wavelength selective element adapted to act upon the input optical signal to produce an output containing a selected subset of the plurality of wavelengths, and as a band-modulo demultiplexer having a free spectral range, the band-modulo demultiplexer being connected to receive the output of the wavelength selective element.
In some embodiments, the wavelength selective element is adapted to produce the output containing the selected subset consisting of an arbitrary subset of wavelengths from the plurality of wavelengths.
In some embodiments, the wavelength selective element is adapted to produce the output containing the selected subset consisting of an arbitrary subset of wavelengths from the plurality of wavelengths subject to a constraint that no two wavelengths in the arbitrary subset are separated by a multiple of the free spectral range.
In some embodiments, the wavelength selective element is adapted to select a contiguous set of wavelengths
In some embodiments, the wavelength selective element is a bandpass filter having a passband.
In some embodiments, the wavelength selective element comprises a bank of components which are individually selectable, each component being adapted to select a respective contiguous set of wavelengths.
In some embodiments, each component is a bandpass filter having a passband.
In some embodiments, a guardband is provided between sets of contiguous wavelengths, and the FSR is substantially equal to a width of the contiguous set of wavelengths plus the guardband.
Another broad aspect of the invention provides an optical wavelength demultiplexer adapted to perform wavelength demultiplexing of an input optical signal containing a plurality of wavelengths. The demultiplexer has a band-modulo demultiplexer having a free spectral range, the band-modulo demultiplexer being connected to receive the input optical signal, and adapted to act upon the input optical signal to produce a plurality of intermediate output signals each containing one or more of the plurality of wavelengths each separated by the free spectral range. For each of at least one of the plurality of intermediate output signals, there is a respective wavelength selective device adapted to produce a selected subset of the intermediate output signal""s one or more wavelength channels.
In some embodiments, each wavelength selective device comprises at least one component adapted to pass a contiguous band of wavelengths.
In some embodiment, the component is a bandpass filter.
In some embodiments, the wavelength selective devices comprise a plurality of static bandpass filters which are individually selectable, each bandpass filter having a passband width substantially equal to the free spectral range of the band-modulo demultiplexer.
In some embodiments, the wavelength selective devices comprise a plurality of static bandpass filters which are individually selectable, with a guardband being defined between a passband of each bandpass filter, such that for each filter, the guardband plus passband width is substantially equal to the free spectral range of the band-modulo demultiplexer.
In some embodiments, each wavelength selective device comprises a tuneable bandpass filter having a passband width less than the free spectral range of the band-modulo demultiplexer thereby allowing a guard band between bands of wavelengths.
In some embodiments, each wavelength selective element is adapted to filter an arbitrary subset of wavelengths from the plurality of wavelengths subject to a constraint that no two wavelengths are separated by a multiple of the free spectral range.
Another broad aspect of the invention provides an optical wavelength demultiplexer adapted to perform wavelength demultiplexing of an input optical signal containing a plurality of wavelengths. The demultiplexer has a fixed wavelength selective element adapted to act upon the input optical signal to produce an output containing a selected subset of the plurality of wavelengths and has a band-modulo demultiplexer having a free spectral range, the band-modulo demultiplexer being connected to receive the output of the wavelength selective element.
Another broad aspect of the invention provides an optical wavelength demultiplexer adapted to perform wavelength demultiplexing of an input optical signal containing a plurality of wavelengths. The demultiplexer has a wavelength selective element adapted to act upon the input optical signal to produce an output containing a selected subset of the plurality of wavelengths, the wavelength selective element comprising a plurality of components each adapted to select a respective subset of the plurality of wavelengths, and switching circuitry for selecting one of the plurality of components to be active at a given time; and a band-modulo demultiplexer having a free spectral range, the band-modulo demultiplexer being connected to receive the output of the wavelength selective element.
Another broad aspect of the invention provides an optical wavelength demultiplexer adapted to perform wavelength demultiplexing of an input optical signal containing a plurality of wavelengths. The multiplexer has a tuneable wavelength selective element adapted to act upon the input optical signal to produce an output containing a selected subset of the plurality of wavelengths; a band-modulo demultiplexer having a free spectral range, the band-modulo demultiplexer being connected to receive the output of the wavelength selective element.
Another broad aspect of the invention provides an optical wavelength multiplexer adapted to perform wavelength multiplexing of a plurality of input optical signals each containing a plurality of wavelengths. The multiplexer has a band-modulo multiplexer having a free spectral range, the band-modulo multiplexer having a plurality of inputs with one input for each of the plurality of input optical signals, the band-modulo multiplexer producing a multiplexed output signal, the band-modulo multiplexer being adapted to combine as the multiplexed output signal for each input any input optical wavelengths in a respective predetermined set of possible wavelengths, each possible wavelength in the set being separated by the free spectral range.